Conventionally, electronic circuit boards were manufactured by mounting electronic parts on the substrate placed and held in the conveying carrier and the substrate heated to the predetermined temperature in the reflow oven. To prevent the occurrence of deflection in the substrate due to thermal stresses during reflow and to improve the yield of the electronic circuit boards during this manufacturing stage, the technology, for instance, disclosed in the Japanese Unexamined Patent Application, First Publication No. 2003-142898, of holding down arbitrary locations of the fringes and the central part of the substrate in close contact with the conveying carrier to prevent the board from being raised above the conveying carrier, was used.
However, when manufacturing the electronic circuit boards using thin printed circuit boards such as thin PWB or FPC substrate, the method of coating resin material with low adhesiveness on the base material of the conveying carrier, and holding the substrate by the adhesive force of the resin material, or the method of fixing the conveying carrier using tape or weight on the fringes of the substrate, were often adopted.
The methods mentioned above bad issues however, such as the ones described below. Firstly, in the method of adhesion and holding of the substrate, the force occurring due to thermal stresses during reflow of the substrate sometimes exceeds the adhesive force of the conveying carrier, and the deflection in the substrate cannot be prevented. Moreover, in the method for fixing the substrate using tape or weight, the costs may increase because of the increase in the man-hours. Furthermore, when a metallic weight is used, this weight absorbs heat during reflow. As a result, the temperature distribution of the substrate surface becomes non-uniform, which may cause unevenness in the molten solder.
Particularly in recent years, with the increasing use of small data recording media and IC cards by general consumers, the demand for electronic circuit boards using very thin substrates has grown rapidly. In these electronic circuit boards, halogen-free substrates and lead-free solder are often used based on the environmental measures mainly adopted in Europe. However, in view of these measures, deflection occurs comparatively easily during reflow in halogen-free substrates, and the melting temperature of lead-free solder is comparatively high; therefore, these measures are disadvantageous considering deflection prevention of substrates. Furthermore, there is a trend these days to make the substrates used in such electronic circuit board thinner, and the cost of these substrates also creates very severe conditions for their manufacture.
The present invention has the object of preventing deflection during reflow of substrate by effectively using existing mounting lines and devices and by restricting costs after considering the circumstances mentioned above.